opts.numepochs =   1;
opts.batchsize = 100;
opts.momentum  =   0;
opts.alpha     =   1;

try
    load(dbn_name);       
catch
    clear dbn
    dbn.sizes = [500 250 30];
    dbn = dbnsetup(dbn, feature, opts);
    save(dbn_name,'dbn');
end